Catalytic converter



July 10, 1962 K. F. PIETZSCH CATALYTIC CONVERTER Filed April 29, 1957 INVENTOR. M 5*. PW BY jyaiean' 0W United States Patent f 3,043,651 CATALYTIC CONVERTER Kurt F. Pietzsch, 3248 Pinehurst Ave., Pittsburgh 16, Pa. Filed Apr. 29, 1957, Ser. No. 655,832 4 Claims. (Cl. 23-1) This invention relates to method of and apparatus for carrying out exothermic reactions by vapor phase catalytic oxidation of organic compounds to produce phthalic anhydride, maleic anhydride and/or other products.

It is a primary object of this invention to provide an improved catalytic converter for passing vapor air mixtures through tubes containing granular catalyst in which the temperature regulation is effected by a large volume bath circulation or coolant on the outside of the catalyst tubes with the continuous addition of relatively small amounts of cooled coolant and the removal of like amounts of hot cooling liquid.

It is a further object of this invention to provide a catalytic converter capable of close temperature control in large capacity production units in which units the reaction is completed and in which the desired product is safely obtained without the addition of excess air for maintaining the organic vapor air mixture entering the converter below its lower explosive limit.

Another object of the invention is the provision of a tubular catalytic converter in which the arrangement of the catalyst tubes, the tube sheets, the bath impelling and bathe means, the height or level of the bath and the inlet and outlet provide maximum output or production capacity while maintaining a desirable low temperature gradient.

These and other objects of the invention will become more apparent from a consideration of the accompanying drawing constituting a part hereof in which like reference characters designate like parts and in which:

FIGURE 1 is a vertical section, partially in elevation, of a tubular catalytic converter embodying the principles of this invention;

FIGURE 2, a top plan view of a screen section taken along the line 2-2, FIGURE 1; and

FIGURE 3, a top plan view of a portion of a tube sheet showing an improved arrangement of the tube perforations taken along the line 3-3, FIGURE 1.

In the drawing the numeral 1 designates a cylindrical shell having an upper and lower tube sheet 2 and 3, respectively, for receiving catalyst tubes 4, the ends of which are welded into the tube sheets in the conventional manner. As shown in FIGURE '3, the perforations 2a and 3a for the tubes 4 are spaced in a manner novel to obtain a practically even radial flow of the coolant. To this end the centers of the outer tubes are arranged on a circle concentric with the converter shell 1, then the next row on a smaller circle with tubes staggered. Following this pattern with an ever decreasing number of tubes in the tube center circles as shown in the drawing, the spacing between the tubes permits the coolant to flow in a radial direction at a substantially constant velocity. The tubes are not shown on the left side of FIGURE 1 to better illustrate the baffle arrangement.

A converter head 5 having a top cover or end wall 6 forms an inlet compartment with the upper tube sheet 2 having an inlet pipe 7. A bottom converter head 8 is provided with an end wall 9 which forms an outlet compartment with the lower tube sheet 3 having an outlet pipe 10. A safety flange 11 on cover 6 secures a rupture diaphram 12 and a vent 13. Segment shaped screen sections 14 are arranged in overlapping relation to close the lower ends of the catalyst tubes 4. The screen sections overlap slightly on the straight radial edges to assure complete coverage of the ends of the tubes. A layer 3,043,651 Patented July 10, 1962 ice of inert granules 15 of substantially the thickness of tube sheet 3 is placed in each tube and rests. upon screen segments 14. The catalyst material 16 is placed on top of the granules 15 to form the catalyst bed. A layer 17 of inert granules is placed on top of the catalyst 16, as shown.

The space within the shell '1 below the tube sheet 2 outside the catalyst tubes 4 contains the cooling liquid or converter bath designated A which, for example, may consist of a mixture of molten nitrates and nitrites of sodium and potassium, having a melting point of between and C. Other mixtures like molten metal may also be used as the coolant. It is of prime importance to the successful operation of the tube converter to employ a large volume coolant circulation at substantially uniform velocity in both horizontal and vertical directions, which is maintained at suitable temperature by addition of a comparable small amount of coolant that has been cooled, for example, 100 or 150 C. outside of the converter. The external coolant supply means and internal bafile arrangement for circulating the coolant consists of the following:

A draft tube 18 is mounted at the vertical center line of the converter having a propeller 19 for circulating the coolant upward. A horizontal baffle 20 extends radially from draft tube 18 to form a horizontal flow pass for the coolant with tube sheet 3 as shown by the directional arrows. A cylindrical wall or vertical flow bafile 21 at the outer edge of baffle 20 forms, with the shell, the outer vertical pass for the coolant circulation. A cylinder or draft tube 22 of smaller diameter than cylinder 21 is mounted concentric with draft tube 18 above horizontal baffie 20. Cylinder 22 forms the vertical middle pass with bafile 21 and with draft tube 18 the inner vertical pass.

The propeller 19 is driven by a motor driven gear reduction mechanism 23 supported on bracket 24 and plate 25 at the top of the converter. Plate 25 is secured to short tube 26 welded to tube sheet 2. from which it extends upward through cover 6 to which it is connected by flange 27. A propeller shaft 28 extends downward from drive 2'3 through sleeve 29 in which it is journalled by bearing 30. Sleeve 29 is supported by sleeve 31 of larger diameter that is secured to plate 25-. Spacing collars 32 and 33 close off a space between sleeves 2.9 and 31 forming a fluid chamber which communicates at the top with conduit '34 leading through plate 25 to a source of cooled coolant. The bottom of the chamber is provided with radial pipes 35 closed at their ends having openings 36 of selected number and size through which the cooled coolant flows to mix with the circulating bath A.

The cooled coolant flowing past propeller shaft hearing 30 keeps the temperature of the bearing below the temperature of the circulating bath A inside the converter. Where the temperature of the coolant A is maintained at 450 C. or higher, the corrosive action of the coolant may require stainless steel construction. Cooling the bear ing as described permits the use of non-stainless bearing materials. If the cooled coolant is not employed to cool the propeller shaft bearing it may be fed into the circulating bath while passing through the center space of the converter in any suitable manner other than described as for example by a pipe extending through the bottom of tube sheet 3 at the center thereof, the only requirement. being that the cooled coolant is completely diffused before leaving the draft tube so that no cold spots may occur in any of the catalyst tubes.

An amount of coolant equal to that delivered to the converter by conduit 34 is removed from the bath A in the following manner.

The top of the converter shell 1 is provided with an 3 expansion joint 37 thatextends below the upper edge 38 of the shell forming a large circular weir for the coolant overflow as shown. A discharge pipe 39 extends inside the converter and passes further down to the outside.

The operation of the above-described converter is briefly as follows:

For example, to produce phthalic anhydride from naphthalene, napthalene Vapors mixed with compressed air enter the converter through inlet pipe 7 into the inlet compartment above tube sheet 2 at a temperature of about 150 C., then pass downward into tubes 4 where initial preheating takes place, which is enhanced by the presence of the inert granules 17. The vapors and compressed air then pass through the catalyst bed 16 in which the naphthalene reacts with part of the oxygen of the air forming phthalic anhydride and some by-products. The maximum temperature in the catalyst is in the neighborhood of 500 C. The formed vapors and gases pass through the lower inert granule layer 15, through screen section 14 into the outlet compartment below tube sheet 3 through outlet pipe to gas cooling and phthalic anhydride condensing equipment.

To maintain suitable working temperature conditions, the propeller drive 23 is energized and propeller 19 moves the coolant upward in draft tube 18, hence downward in the inner pass around the lower edge of draft tube 22 upward in the middle pass over the edge of bafiie 21 and downward in the outer pass and back through the horizontal pass below bafile to the draft tube 18, as shown by the arrows in FIGURE 1 of the drawing.

The bath circulating on the outside of the catalyst tubes absorbs the heat created by catalytic reaction inside the tubes, which is in large converters, over 10 million B.t.u. and to avoid a temperaure rise of more than about 10 degrees C., a large volume of coolant has to be circulated.

The tube and baflie arrangement shown in FIGURE 1 permits fast flow of the coolant with minimum flow resistance. Low flow resistance is necessary for maintaining the liquid level below the underside of the tube sheet 2, as shown, to avoid contact with the tube sheet and raising the temperature of the tube sheet to that of the coolant and the liquid level must not vary more than a.

few inches. As shown, the surface of the bath or coolant is higher in the center of the converter than near the shell. For example, at the center it may be 8 inches be low the upper tube sheet 2, while at the shell or outer edge of the converter it maybe 12 inches below the tube sheet. Flow resistance is also reduced to a minimum by spacing the tubes in the manner shown in FIGURE 3 of the drawing, as heretofore explained. By thus arranging the tubes and by the arrangement of the battles as shown, the velocity of the coolant flowing vertically through the passes and horizontally through the narrow spaces between the tubes is substantially the same throughout the converter. By maintaining the liquid level higher on the inside of draft tube 22 over the level on the outer side, as shown at A, the coolant moves from the one side of draft tube 22 around its lower edge to the other side, as shown by the arrows.

The hot coolant, leaving the converter through pipe 39 is being cooled down, say 100 to 150 degrees C. and is pumped back in amounts controlled by the temperature of the bath in the converter. quantities being circulated by the propeller and the quantitles for cooling added through pipe 34, the production of maleic anhydride in a unit into which 3000 lbs. per hour of benzene vapors are fed, is assumed. In producing maleic anhydride, catalytically, the exotherm is extremely high and over million Btu. would have to be removed by the coolant. Circulating about 12,000 gallons per minute by the propeller, the temperature of the coolant circulating around the catalyst tubes is, within about 6 degrees C., the same throughout the converter. Adding coolant, cooled down about 100 degrees C., or more, the

To illustrate, the coolant '4 circulating coolant would require less than 600 gallons per minute coolant addition.

Although the invention has been described in connection with the production of phthalic anhydride and maleic anhydride, it will be apparent that the converter may be applied in producing other products by vapor phase catalytic oxidation of organic compounds.

I claim:

1. In a converter for carrying out exothermic reactions by vapor phase catalysis in the form of an outer shell having a pair of tube sheets mounted in vertically spaced relation to form a chamber therebetween for circulating cooling fluid and having catalyst tubes mounted between said tube sheets and communicating at their ends with inlet and outlet passages outside of said chamber in which the chamber between said tube sheets has inlet and outlet passages for the continuous flow of a cooling liquid with means for causing said cooling liquid to circulate between said tube sheets and for controlling the rate of flow thereof and in which a central draft tube is placed vertically in the center of the converter with its top disposed a distance from the upper tube sheet to provide adequate space for a coolant being propelled upward in said draft tube to discharge radially into the spaces between the surrounding catalyst tubes, the said chamber having an outwardly extending horizontal baffle at the lower end of the central draft tube terminating at its outer periphery in an outer draft tube, which is a large diameter vertical draft tube that extends upward concentrically with the central draft tube terminating at its upper end at a distance from the upper tube sheet essentially the same as the distance of the top of the central draft tube from the same tube sheet, the space above said horizontal bafile being open and an intermediate draft tube placed concentrically between the central draft tube and outer draft tube extending upward forming a flow barrier and with its lower end terminating at adequate distance from said horizontal battle to cause the coolant discharging from the top of the central draft tube to pass through the spaces between the catalyst tubes in the section above said horizontal baflle in a sinuous path on its Way to an outer flow passage, the combination with a propeller within said central draft tube, mounted on a shaft, axially centered in said central draft tube and supported on top of the converter, of a sleeve in said central draft tube coaxial with said propeller shaft having radial arms at the lower end thereof, said sleeve being provided with a partition to form a flow chamber communicatiing with an inlet passage for receiving a cooled cooling fluid, and said arms having perforations for the escape of said fluid into the mixing chamber formed by the top section of the central draft tube above said propeller, said radial arms disposed closely above the propeller being located in said central draft tube at adequate distance from the top of the central draft tube to obtain turbulent mixing of the cooled coolant with the circulating coolant in the mixing chamber to uniformly cool the cooling liquid discharging from the top of said mixing chamber into the spaces between the catalyst tubes, said propeller shaft being journalled by a bearing disposed within said radial arms which bearing is maintained at a safe operating temperature by the coolant passing through theflow chamber of the propeller shaft supporting sleeve into the mixing chamber, and means for withdrawing some of the cooling liquid from the top of said circulating chamber at the same rate as the amount of cooling liquid delivered through said inlet passage.

2. Apparatus as set forth in claim 1 in which the sleeve in the central draft tube is blocked off to constitute a flow chamber, having an inlet connection with a source of cooled coolant outside of the converter.

3. Apparatus as set forth in claim 1 in which the cooled cooling fluid is continuously delivered and added to the liquid in the circulating chamber from a source outside 5 of said chamber in controlled amounts at temperatures substantially below the temperature of the cooling liquid in said chamber, and cooling; liquid is continuously withdrawn from said last named chamber in the same amount as the cooled coolant added to the liquid in said chamher.

4. In the method of maintaining substantially uniform cooling throughout the reaction zone of a converter in which heat liberating catalytic reaction takes place between substances in the vapor phase in catalyst tubes at constant elevated temperatures, the steps which consist of continuously passing a large volume of cooling liquid of predetermined temperature from the axial center of the converter into the spaces between the catalyst tubes and cooling the circulating cooling liquid by continuously delivering into the circulating stream of cooling liquid controlled amounts of the same cooling liquid at temperatures substantially below the temperature of the circulating cooling liquid while constantly removing a like amount of the circulating cooling liquid from the converter.

References Cited in the file of this patent UNITED STATES PATENTS 964,936 Pownall July 19, 1910 1,627,450 Otis May 3, 1927 1,812,341 Iaeger June 30, 1931 1,905,719 Jaeger Apr. 25, 1933 1,909,358 Jaeger May 16, 1933 1,917,718 Iewett July 11, 1933 1,936,610 Thomas Nov. 28, 1933 2,042,632 Reynolds June 2, 1936 2,198,555 Wilson Apr. 23, 1940 FOREIGN PATENTS 963,913 France Ian. 18, 1950 

1. IN A CONVERTER FOR CARRYING OUT EXOTHERMIC REACTIONS BY VAPOR PHASE CATALYSIS IN THE FORM OF AN OUTER SHELL HAVING A PAIR OF TUBE SHEETS MOUNTED IN VERTICALLY SPACED RELATION TO FORM A CHAMBER THEREBETWEEN FOR CIRCULATING COOLING FLUID AND HAVING CATALYST TUBES MOUNTED BETWEEN SAID TUBE SHEETS AND COMMUNICATING AT THEIR ENDS WITH INLET AND OUTLET PASSAGES OUTSIDE OF SAID CHAMBER IN WHICH THE CHAMBER BETWEEN SAID TUBE SHEETS HAS INLET AND OUTLET PASSAGES FOR THE CONTINUOUS FLOW OF A COOLING LIQUID WITH MEANS FOR CAUSING SAID COOLING LIQUID TO CIRCULATE BETWEEN SAID TUBE SHEETS AND FOR CONTROLLING THE RATE OF FLOW THEREOF AND IN WHICH A CENTRAL DRAFT TUBE IS PLACE VERTILOW CALLY IN THE CENTER OF THE CONVERTER WITH ITS TOP DISPOSED A DISTANCE FROM THE UPPER TUBE SHEET TO PROVIDE ADEQUATE SPACE FOR A COOLANT BEING PROPELLED UPWARD IN SAID DRAFT TUBE TO DISCHARGE RADIALLY INTO THE SPACED BETWEEN THE SURROUNDING CATALYST TUBES, THE SAID CHAMBER HAVING AN OUTWARDLY EXTENDING HORIZONTAL BAFFLE AT THE LOWER END OF THE CENTRAL DRAFT TUBE TERMINATING AT ITS OUTER PERIPHERY IN AN OUTER DRAFT TUBE, WHICH IS A LARGE DIAMETER VERTICAL DRAFT TUBE EXTENDS UPWARD CONCENTRICALLY WITH THE CENTRAL DRAFT TUBE TERMINATING AT ITS UPPER END AT A DISTANCE FROM THE UPPER TUBE SHEET ESSENTIALLY THE SAME AS THE DISTANCE OF THE TOP OF THE CENTRAL DRAFT TUBE FROM THE SAME TUBE SHEET, THE SPACE ABOVE SAID HORIZONTAL BAFFLE BEING OPEN AND AN INTERMEDIATE DRAFT TUBE PLACED CONCENTRICALLY BETWEEN THE CENTRAL DRAFT TUBE AND OUTER DRAFT TUBE EXTENDING UPWARD FORMNG A FLOW BARRIER AND WITH ITS LOWER END TERMINATING AT ADEQUATE DISTANCE FROM SAID HORIZONTAL BAFFLE TO CAUSE THE COOLANT DISCHARGING FROM THE TOP OF THE CENTRAL DRAFT TUBE TO PASS THROUGH THE SPACES BETWEEN THE CATALYST TUBES IN THE SECTION ABOVE SAID HORIZONTAL BAFFLE IN A SINUOUS PATH ON ITS WAY T AN OUTER FLOW PASSAGE, THE COMBINATION WITH A PROPELLER WITHIN SAID CENTRAL DRAFT TUBE, MOUNTED ON A SHAFT, AXIALLY CENTERED IN SAID CENTRAL DRAFT TUBE AND SUPPORTED ON TOP OF THE CONVERTER, OF A SLEEVE IN SAID CENTRAL DRAFT TUBE COXIAL WITH SAID PROPELLER SHAFT HAVING RADIAL ARMS AT THE LOWER END THEREOF, SAID SLEEVE BEING PROVIDED WITH A PARTITION TO FORM A FLOW CHAMBER COMMUNICATING WITH AN INLET PASSAGE FOR RECEIVING A COOLED COOLING FLUID, AND SAID ARMS HAVING PERFORATIONS FOR THE ESCAPE OF SAID FLUID INTO THE MIXING CHAMBER FORMED BY THE TOP SECTION OF THE CENTRAL DRAFT TUBE ABOVE SAID PROPELLERM SAID RADIAL ARMS DISPOSED CLOSLEY ABOVE THE PROPELLER BEING LOCATED IN SAID CENTRAL DRAFT TUBE AT ADEQUATE DISTANCE FROM THE TOP OF THE CENTRAL DRAFT TUBE TO OBTAIN TURBULENT MIXING OF THE COOLED COOLANT WITH THE CIRCULATING COOLANT IN THE MIXING CHAMBER TO UNIFORMLY COOL THE COOLING LIQUID DISCHARGING FROM THE TOP OF SAID MIXING CHAMBER INT THE SPACES BETWEEN THE CATALYST TUBES, SAID PROPELLER SHAFT BEING JOURNALLED BY A BEARING DISPOSED WITHIN SAID RADIAL ARMS WHICH BEARING IS MAINTAINED AT A SAFE OPERATING TEMPERATURE BY THE COOLANT PASSING THROUGH THE FLOW CHAMBER OF THE PROPELLER SHAFT SUPPORTING SLEEVE INTO THE MIXING CHAMBER, AND MEANS FOR WITHDRAWING SOME OF THE COOLING LIQUID FROM THE TOP OF SAID CIRCULATING CHAMBER AT THE SAME RATE AS THE AMOUNT OF COOLING LIQUID DELIVERED THROUGH SAID INLET PASSAGE.
 4. IN THE METHOD OF MAINTAINING SUBSTANTIALLY UNIFORM COOLING THROUGHOUT THE REATION ZONE OF A CONVERTER IN WHICH HEAT LIBERATING CATALYTIC REACTION TAKES PLACE BETWEEN SUBSTANCES IN THE VAPOR PHASE IN CATALYST TUBES AT CONSTANT ELEVATED TEMPERATURES, THE STPS WHICH CONSIST OF CONTINUOUSLY PASSING A LARGE VOLUME OF COOLING LIQUID OF PREDETERMINED TEMPERATURE FROM THE AXIAL CENTER OF THE CONVERTER INTO THE SPACES BETWEEN THE CATALYST TUBES AND COOLING THE CIRCULATING COOLING LIQUID BY CONTINUOUSLY DELIVERING INTO THE CIRCULATING STREAM OF COOLING LIQUID CONTROLLED AMOUNTS OF THE SAME COOLING LIQUID AT TEMPERATURES SUBSTANTIALLY BELOW THE TEMPERATURE OF THE CIRCULATING COOLING LIQUID WHILE CONSTANTLY REMOVING A LIKE AMOUNT OF THE CIRCULATING COOLING LIQUID FROM THE CONVERTER. 